Apicomplexa
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2008-06-20T16:25:56Z
165.230.31.178
{{Taxobox
| name = Apicomplexa
| image = Malaria.jpg|Plasmodium
| domain = [[Eukaryota]]
| regnum = [[Chromalveolata]]
| superphylum = [[Alveolata]]
| phylum = '''Apicomplexa'''
| subdivision_ranks = Classes & Subclasses
| subdivision =
'''[[Aconoidasida]]'''<br />
*[[Haemosporasina]]<br />
*[[Piroplasmasina]]<br />
'''[[Blastocystis hominis|Blastocystea]]'''<br />
'''[[Conoidasida]]'''<br />
*[[Coccidia|Coccidiasina]]<br />
*[[Gregarinasina]]<br />
}}
The '''Apicomplexa''' are a large group of [[protist]]s, characterized by the presence of a unique [[organelle]] called an ''apical complex'' (see also [[apicoplast]]). They are unicellular, spore-forming, and exclusively parasites of animals. Motile structures such as [[flagellum|flagella]] or [[pseudopod]]s are absent except in certain [[gamete]] stages. This is a diverse group including organisms such as [[coccidia]], [[gregarine]]s, [[piroplasm]]s, [[haemogregarine]]s, and [[malaria]]s; some diseases caused by apicomplexan organisms include:
* [[Babesiosis]] (''[[Babesia]]'')
* [[Malaria]] (''[[Plasmodium]]'')
* [[Cryptosporidiosis]] (''[[Cryptosporidium]]'')
* [[Coccidia]]n diseases including:
** [[Cryptosporidiosis]] (''[[Cryptosporidium parvum]]'')
** [[Cyclosporiasis]] (''[[Cyclospora cayetanensis]]'')
** [[Toxoplasmosis]] (''[[Toxoplasma gondii]]'')
Most members have a complex life-cycle, involving both asexual and sexual reproduction. Typically, a host is infected via an active invasion by the parasites (similar to [[entosis]]), which divide to produce ''[[sporozoite]]s'' that enter its cells. Eventually, the cells burst, releasing ''[[merozoites]]'' which infect new cells. This may occur several times, until ''gamonts'' are produced, forming gametes that fuse to create new cysts. There are many variations on this basic pattern, however, and many Apicomplexa have more than one host.
[[Image:Apicomplexa_life_cycle_v2.svg|thumb|left|280px|Generic life cycle of an apicomplexa: 1-[[zygote]] ([[Microbial cyst|cyst]]), 2-[[sporozoite]]s, 3-[[merozoite]]s, 4-[[gametocyte]]s.]]
[[Image:Apicomplexa_structure.svg|thumb|left|280px|Apicomplexan structure: 1-polar ring, 2-conoid, 3-micronemes, 4-rhoptries, 5-nucleus, 6-nucleolus, 7-mitochondria, 8-posterior ring, 9-alveoli, 10-golgi apparatus, 11-micropore.]]
The apical complex includes vesicles called [[rhoptries]] and [[microneme]]s, which open at the anterior of the cell. These secrete enzymes that allow the parasite to enter other cells. The tip is surrounded by a band of [[microtubule]]s, called the polar ring, and among the Conoidasida there is also a funnel of rods called the conoid..<ref name=coccidiaworld>{{cite web
|url=http://biology.unm.edu/biology/coccidia/home.html
|title=The Coccidia of the World
| last = Duszynski1
| first = Donald W.
| coauthors = Steve J. Upton and Lee Couch
| work =
| publisher = Department of Biology, University of New Mexico, and Division of Biology, Kansas State University
| date = 2004-02-21
| format = Online database }}</ref> Over the rest of the cell, except for a diminished mouth called the micropore, the membrane is supported by vesicles called alveoli, forming a semi-rigid pellicle.
The presence of alveoli and other traits place the Apicomplexa among a group called the [[alveolate]]s. Several related flagellates, such as ''[[Perkinsus marinus|Perkinsus]]'' and ''Colpodella'' have structures similar to the polar ring and were formerly included here, but most appear to be closer relatives of the [[dinoflagellate]]s. They are probably similar to the common ancestor of the two groups.
Another similarity is that apicomplexan cells contain a single [[plastid]], called the [[apicoplast]], surrounded by either 3 or four membranes. Its functions are thought to include tasks such as lipid synthesis, it appears to be necessary for survival. They are generally considered to share a common origin with the chloroplasts of dinoflagellates, although some studies suggest they are ultimately derived from [[green alga|green]] rather than [[red algae]].
The Apicomplexa comprise the bulk of what used to be called the Sporozoa, a group for parasitic protozoans without flagella, pseudopods, or cilia. Most of the Apicomplexa are motile however. The other main lines were the [[Ascetosporea]], the [[Myxozoa]] (now known to be derived from [[animal]]s), and the [[Microsporidia]] (now known to be derived from [[fungus|fungi]]). Sometimes the name Sporozoa is taken as a synonym for the Apicomplexa, or occasionally as a subset.
== Blood borne genera ==
Within the Apicomplexa there are three groups of blood borne parasites. These species lie within in three suborders.
* suborder [[Adeleorina]] - 8 genera
* suborder [[Haemosporina]] - all genera in this suborder
* suborder [[Eimeriorina]] - 2 genera (''[[Lankesterella]]'' and ''[[Schellackia]]'')
Blood parasites belonging to the suborder Adeleorina are collectively known as haemogregarines. Currently their sister group is thought to be the [[piroplasm]]s.
Suborder Adeleorina has ~400 species and has been organised into four large and 4 small genera.
The larger genera are:
*family [[Haemogregarinidae]] - taxon created by Neveu-Lemaire in [[1901]]
genera:
*''[[Haemogregarina]]'' - taxon created by Danilewsky in [[1885]]
*''[[Cyrilia]]'' - taxon created by Lainson in [[1981]]
*family [[Karyolysidae]] - taxon created by Wenyon in [[1926]]
genera:
*''[[Karyolysus]]'' - taxon created by Labbe in [[1894]]
*family [[Hepatozoidae]] - taxon created by Wenyon in [[1926]]
genera:
*''[[Hepatozoon]]'' - taxon created by Miller in [[1908]]
The smaller genera are :
*''[[Hemolivia]]'' - taxon created by Petit ''et al'' in [[1990]]
*''[[Desseria]]'' - taxon created by Siddall in [[1995]]
*family [[Dactylosomatidae]]
genera:
*''[[Dactylosoma]]''
*''[[Babesiosoma]]''
Notes:
Species of the genus ''Desseria'' infect fish and lack erythrocytic [[merogony]].
The species of the genera ''Dactylosoma'' and ''Babesiosoma'' infect [[fish]] and [[reptile]]s.
[[Leech]]es are the only known [[Vector (biology)|vector]]s for these species and their [[vertebrate]] hosts are aquatic.
== Disease Genomics ==
As noted above, many of the apicomplexan parasites are important pathogens of human and domestic animals. In contrast to [[bacteria]]l pathogens, these apicomplexan parasites are [[eukaryote]]s and share many metabolic pathways with their animal hosts. This fact makes therapeutic target development extremely difficult – a drug that harms an apicomplexan parasite is also likely to harm its human host. Currently there are no effective [[vaccine]]s or treatments available for most diseases caused by these parasites. Biomedical research on these parasites is challenging because it is often difficult, if not impossible, to maintain live parasite cultures in the laboratory and to genetically manipulate these organisms. In the recent years, several of the apicomplexan species have been selected for [[genome sequencing]]. The availability of [[genome]] sequences provides a new opportunity for scientists to learn more about the [[evolution]] and biochemical capacity of these parasite. A [[NIH]]-funded database, [http://ApiDB.org ApiDB.org], provides public access to currently available genomic data sets.
== References ==
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== External links ==
*{{cite web
| coauthors = S.J. Brands (Compiler)
| title = The Taxonomicon & Systema Naturae
| work = Taxon: Genus Cryptosporidium
| publisher = Universal Taxonomic Services, Amsterdam, The Netherlands
| date = 2000
| url = http://www.taxonomy.nl/taxonomicon/
| format = Website database }}
[[Category:Parasitic protists]]
[[Category:Apicomplexa|*]]
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